The invention relates to a drive device for a vehicle roof cover that can be adjusted between end positions, with an electric motor that is connected by a reduction gear to a driving pinion located on a drive shaft, a driving pinion which is connected to the vehicle part so as to drive it, as well as to a switching device controlling the motor to stop the motor in at least one predetermined position of the vehicle part. More specifically, the invention relates to such a drive device where a switch wheel is provided to actuate the switching device, and during adjustment of the vehicle part between its end positions, an eccentric gear train causes the switch wheel to rotate less than 360.degree., the eccentric gear train having an external gear with an internal toothing, that is coaxial to a common shaft of the reduction gear and eccentric gear train, and an internal gear that has an external toothing meshed with the internal toothing and at least one tooth less than the external gear, and that is supported on an eccentric disk that is connected to the shaft in a manner permitting relative rotation between the internal gear and eccentric disk.
In known drive devices of this type U.S. Pat. No. 4,468,063, U.S. Pat. No. 4,659,141 and U.S. Pat. No. 4,561,691, the external gear of the eccentric gear train is integrally connected with a transmission housing part; in particular, it is formed on the transmission housing part. When the eccentric disk rotates, the internal gear is caused to rotate relative to the external gear. During this rotation, the switch wheel is slaved by a pin that is attached to the internal gear and that engages in a radial slot of the external gear to allow the rotation of the internal gear. When the connection between the relevant transmission housing part and the external gear is of a one-piece construction, the combination of transmission housing part and external gear represents a relatively expensive precision component. If the transmission housing part and the external gear are manufactured as separate components, an overall multipart drive device results, whose assembly is relatively expensive.
In other known drive devices for adjustable covers of vehicle roofs (Gebrauchsmuster 76 29 034 and U.S. Pat. No. 4,420,185), a stepping gear is provided instead of an eccentric gear train. But for the purpose at hand, suitable stepping gears require expensive, highly precise components. Tolerances for the gears are strict. Further, during operation, undesired clicking noises result because of intermittent tooth engagement.